I agree with John. The general rule on grounding and bonding is you size the grounding conductor based on the circuit that is likely to energize the protected equipment. In your case I would say it was the 70a UPS and 250.122 says that is a #8 copper or #6 al. This should be bonded to the EGC of the UPS supply conductors or back to the panel grounding bus, in my opinion.
I suppose you could go to building steel if you can assure that it is effectively bonded back to the grounding system but a water pipe is not usually an acceptable ground these days. Too much plastic in the plumber's trade.
[This message has been edited by gfretwell (edited 11-11-2004).]
